Grinding cam lobes on a cam shaft has usually been achieved by a grinding wheel, which grinds each cam in sequence. In some instances, by resort to complex mechanical machines with two grinding heads, a pair of cams may be ground concurrently.
In response to the needs of automotive manufacturers, in particular, efforts have been made to devise and develop, a reliable grinding machine that will grind, simultaneously, a number of or all of the cams, or lobes, on a camshaft. Since camshafts are a costly and complex article of manufacture, and since the costs of manufacturing same are significant, diverse approaches have been considered to move, technically, beyond the well known techniques relying upon grinding wheels.
One alternative approach has focused upon the use of abrasive grinding belts in lieu of the conventional grinding wheel. Such approach has considerable potential, for several belts may be utilized, in side-by-side relationship, to grind the several lobes on a camshaft simultaneously. Also, the belts, if mass-produced, will be much lower in cost, and can be discarded, after usage for an extended period of time.
Abrasive grinding belts may have been initially used in Italy ten or more years ago to grind camshafts as illustrated in U.S. Pat. No. 4,175,358, granted Nov. 27, 1979, to Ido Boscheri, which discloses a plunge grinding machine employing several abrasive belts to simultaneously grind all of the cams which are present on a timing shaft for an engine. Such grinding machine includes a massive baseplate (10) which carries a table (12) which can be reciprocated (by jacks 13) with respect to the baseplate, a tail stock and head stock mounted on the table and adapted to support the camshaft (19) to be ground, and a stationary crosspiece (22) carrying a plurality of machining units. Each machining unit comprises a supporting member (31), front and rear heads (32, 33), an abrasive belt (36), jack (43), etc. that are driven by a sensing roller (42) operatively associated with a pattern piece (18) from which the workpiece (cam) to be ground is copied. Separate drive motors (15, 25) are connected through appropriate gear transmissions and couplings so that the workpiece to be ground, and the pattern piece, are rotated in the proper phase relationship.
U.S. Pat. No. 4,833,834, granted May 30, 1989, to Henry B. Patterson et al, discloses several embodiments of multiple belt camshaft grinding machines. Each grinding machine has several grinding belts (28) and a drive (such as main drive pulley 30) therefor, and contouring shoes (35) and support members (pushrods 43) carried on a feed table (12) for separate control of cam contouring and grinding feed rate. The camshaft workpiece (20) is carried on a fixed axis by a table (16) providing axial motion for belt wear balancing oscillation. The grinding operations may be controlled by master cams, as in the embodiment of FIGS. 1 and 2, or may be numerically controlled, as in the embodiments of FIGS. 3 and 6-10.
U.S. Pat. No. 4,945,683, granted Aug. 7, 1990 to James D. Phillips, discloses an apparatus for grinding, to a predetermined contour, a plurality of eccentric cams (L) on a camshaft (W). The apparatus comprises several abrasive belts (58) supported adjacent the cam shaft for linear movement, such that the belts grind the peripheries of the cams (as shown in FIGS. 1 and 8). The belts are guided along a variable path, according to the cam contour desired, by shoes (72) engaging the belts at their point of contact with the cams. The shoes are mounted on actuators (76) powered by motor units (78) controlled by CNC controllers. Each belt passes through a coolant distributor (130) so that coolant saturates each belt and conditions same for better abrading action. The pressure of fluid within each distributor causes the belt to flex, and compensates for the tendency of the belt to stretch as the shoe 72 moves in and out.
U.S. Pat. No. 5,142,827, granted Sep. 1, 1992, to James D. Phillips, discloses a crank pin grinder employing multiple abrasive belts.
The latter three patents reflect the increasing interest in grinding machines employing several abrasive belts, side by side, to grind all of the surfaces, on a workpiece. The market potential available to the manufacturer of a commercially acceptable grinding machine that employs abrasive grinding belts is significant.
The majority of the deficiencies of the foregoing prior art multiple belt grinding machines were addressed, and resolved, by the multiple belt grinding machines disclosed in U.S. patent application Ser. No. 07/953,798, now U.S. Pat. No. 5,359,813, and application Ser. No. 07/953,799, filed Sep. 30, 1992, and presently pending. Such multiple belt grinding machines were characterized, inter alia, by long-lived, endless, abrasive belts that were easily installed, and, when necessary, removed and/or replaced. The grinding machines allowed ready access to the endless belts at two locations spaced along one side of the machine.
At one location, the outboard support bracket for the drive drum assembly is moved laterally, a significant distance, to expose the multiple belts. At a second location, a rotary actuator, with a locking arm, is pivoted through an arc, which may be 45.degree., to reveal the multiple belts affixed to the underside of the contouring head assembly, at the front thereof.
Whereas the drive drum assembly disclosed in U.S. patent application Ser. Nos. 07/953,798 (now U.S. Pat. No. 5,359,813), and 07/953,799, filed Sep. 30, 1992, and both assigned to the assignee of record, Western Atlas Inc., functioned satisfactory, prolonged usage of the multiple belt grinding machines indicated that refinements in the drive drum assembly were desirable. Occasionally, in the field, operators noted chatter and/or vibrations between the central shaft of the drive drum assembly and the corresponding aperture in the movable outboard support that receives one end of the central shaft of the drive drum assembly. The central shaft is supported at the opposite end-by a fixed bearing support.
Such relationships are shown in FIG. 4 of the two applications noted above, wherein the projecting nose is identified by reference numeral 148a, and the central shaft for the drive drum is identified by reference numeral 148. The laterally movable support bracket is indicated by reference numeral 142, the fixed support bearing is indicated by reference numeral 160, and the drive drum assembly is indicated by reference numeral 100.
The projecting nose 148a has a series of flats formed above its periphery. The outer diameter of projecting nose (148a) has a clearance fit with the inner diameter of a spindle in the outboard support bracket (142) to permit engagement, thus creating the possibility of slippage and/or radial shake during operation. Consequently, when the drive belt (104) delivers power to one end of central shaft (148), the radial clearance between the flats and the aperture causes slippage. Also, the central shaft exhibited a tendency to sag, a minute fraction of an inch, in cantilever fashion, due to the loads imposed thereon. While the sagging problem, and/or the slippage problem would normally be minor problems, such problems take on far greater significance when viewed in the context of a high precision, multiple belt, grinding machine, for grinding workpieces with differently shaped surfaces within exceedingly close tolerances. Also, the sagging and/or slippage problems contribute to poor wear characteristics for key components of the grinding machine.